Pyrolysis of pinane



" Patented a. 30, 1945 rrnonrsrs or Alfred L. Bummelsburg, Wilmington, DeL, assignor to Hercules. Powder Comparm'Wilmingtou,

bet, a corporation cl Delaware No Drawing. Application May 15, 194:. Serial No. 407.152 o l m invention relates to a method lng plums and more particularly to a method or producing dihydroacyolic terpenes "by means or the vapor-phase pyro sis or pinane.

Many thermal reactio of unsaturated terpenehydrocarbons are known using various conditions of heating, contact time, type or reaction acne, pressure, and catalyst. However, no prior art is known where saturated terpenes have been treated, especially the saturated bicyclic terpene,

pinane, under conditions to produce a mixture 01" dihydroacyclic terpenes. Dihydroacyclic terpenes have been prepared by means at the reduction or unsaturated acyclic terpenes in alcohol with sodium or other suitable hydrogenation medium. This reduction method at the .present time is impractical because of the comparatively low field of desirable dihydroacyclic terpeues and further, because the method is time-consuming and expensive. 4

Now, in accordance with the present invention, it has been discovered that a useful mixture of isomers oi pinane, particularly dihydroacyclic terpenes may be produced in substantial yields directly irom pinane bytreating the pinane at 35 a temperature above about 400' C.', until conversion is at least partially complete. The method in accordance with this inventio isillustrated by the following specinc examples, 7

all parts and percentages being by weight unless otherwise specified.

Any pinane containing material having a preponderance or pinane may beused and is found suitable in accordance with this invention. Pinane, thestarting material used in each or the ioliowing examples may e prep ed by t e a av lytic hydrogenation of alphaor beta-pinene according to'methods well known in the art, particularly the plnane used inllixampie 1.

Two thousand parts or alpha-pinene were byin the presence or Haney nickel catalyst under a pressure or 1100 to 2000 pounds .per square inch at a temperature of 75 C. to 100 0. until about 19 parts of hydrogen was ab- Example 1 nine number or 1.5 and a refractive index n" 0! 1.4632 were placed in an evaporator flask and heated almost to its boiling point and then carriedtc areaction aonebybubblinsastreamoi jnltrogeuintotheevaporator. 'rnareaeuon eaey scum. (c1. zoo-m) ol-isomerizwas maintained at a temperature between 500 and 560 C. The pinane was passed through the reaction zone at a rate 01' 1.9 parts liquid condensate per minute for 20 minutes. The pyrolyzate had a bromine number of 155 as compared to a bromine number 01 230 for substantially pure dihydroacyclic terpenes and a refractive index n of 1.4499, indicating the presence of a mixture or dihydroacyclic terpenes in an amount or about 67%.

Example 2 Five hundred parts of pinane having a bromine I number of 3 and a refractive index n 01 1.4629 were placed in the evaporator and heated to almost its boiling point and the vapors: carried through the reaction zone at the rate or 2.8 parts liquid condensate per minute for minutes. The reaction zone was heated to a temperature between 430 and 480 C. A supported mildly acidic catalyst was positioned within the reaction zonedirectly in the path of travel or the pinane. The catalyst comprised parts oi pumice (pieces approximately inch cross section) which had been mixed with a solution of parts 01 sodium dihydro-orthophosphate (NaIhPOaHzO) in 64 parts or water for two hours and then dried in an oven at C. for two hours. The pyrolyzate had a bromine number 01 178 and a refractive index 113 at 1.4488, indicating the presence of a mixture or dihydroacyclic terpenes in an amount or about 77%.

Identification of the pprolyzate 1 762.6 mm. of mercury and 760.8 mm. of mercury.

a so. Fivehundredpartsorpinanehavingabrcsecond cut weighed 193 parts oi. the original charge. Analysis or these cuts No. 1 andNo. 2 were as follows;

Outs

I Each of the above cuts was analyzed for unsaturation and it was found that the pyrolyzate was made up of compounds having two double bonds. Seventy parts or out No. 1 were hydro genated using 15 parts of reduced nickel on kieselguhr (16 per cent nickel) as catalyst at 85 to 165 C. and a hydrogen pressure or 1100 towhich theory is calculated to be 2.94% for two double bonds. Tests made with maleic anhydride indicated that the dihydroacyclic terpenes do not contain a conjugated system 01' double bonds.

A comparison of the physical constants determined for the pyrolyzates with physical constants reported in the literature for certain dihydroacyclic terpenes indicates that the pyrolyzates con ain substantially entirely a mixture of'dihy omyrcene (2,6-dimethyl-2,7-octadiene); di-

' hydroallo-ocimene (2,6-dimethyl-2,6-octadiene);

and, 2,6-dimethyl-octadiene-2,5.

The pyrolysis temperature may vary from about 400 C. to about 700 C. The preferred pyrolysis temperature is between about 450 C. to

' about 550 C.

c The pinane va or may be passed through the reaction zone wit out the aid oi a carrier; However, passage of the pinane vapor may be facilitated by means of an inert carrier such asa gas 4 as, for example, steam, carbon dioxide, nitrogen, and other suitable gaseous diluents. It is desirable to pass the pinane vapor through the reaction zone at such a rate that the vapors will be subjected to the heating conditionsv oi the reaction zone for a relatively short period of time as, for example, about 2 to about 20 seconds. Shorter periods of time are to be used at the higher temperatures as, for example, 700 C. and

longer periods 01' time areto be used at the lower temperatures'as, for example, 400 C. in comparison with the general contact time range of 2to about 20 seconds.

The pyrolysis system will desirably consist 01' an evaporator, a preheater, a reaction zone, and a water-cooled condenser. The preheater and reaction zone may be heated in any suitable manner preferably, electrically. The entire system may be constructed of glass or or any durable metal as, tor example, iron, steel, stainless steel, copper, etc. A

The reaction zone may comprise a chamber either'packed with such inert materials as porous chips, pumice. glass, irontumings, etc, or constructed with metal baflles, or thechamber may 55 be used in an unfilled or empty condition. It has been found that under certain conditions of operation it is easier to control the temperature of an empty reaction chamber than one fllled as described above.

1 Catalysts may be used in the reaction chamber and under certain conditions of operation will promote the isomerization of the pinane to a mixture of" dihydroacyclic terpenes by permitting dihydro-orthophosphate,

About 3.24% by perature than is necessary when no catalyst is employed. Mildly acidic catalysts such as sodium sodium monohydro- .orthophosphate, boric acids, etc., may be em- 5 plmed desirably on the surface of an absorbent such as pumice, etc. Other mildly acidic catalysts are found to be operable in accordance with the -present invention. In addition; siliceousmateg rials such as silica gel, magnesium silicate,cal-

cium silicates, etc., may be employed.

The dihydroaicyclic terpenes obtained in accordance with thee present invention boil in the range between about 158*0. andabout-163 C.

taken at 760 mm. pressure of mercury. The re-' fractiveindex 113 0! a mixture of the diliydroacyclic terpenes varies between about 1.440 and about 1.454. The density d4" of the mixture of dihydroacyclic terpenes varies between about 0.765 and about 0.805. The bromine number 0! the dihydroacyclic terpene mixture varies between'about 190 and about 230. v

The mixture of dihydroacyclic terpenes produced in accordance with the present invention is useful in producing high yields of lower moactions.

It is apparent, in view of the foregoing disclosure, that a new process has been discovered for producing a mixture of dihydroacyclic terpenes having a boiling point in the range between about 158 C. and about 163 C-.,- and having a refractive index n between about 1.438

and about 1.453 and having a density d4 between about 0.765 and about 0.805 which comprises heating pinane to a temperature between about 400 C. and about 700 C. until isomerization of the pinane is at least partially complete.

What I claim and desire to protect by Letters Patent is:

0 l. A method of isomerizing pinane to a mixture of dihydroacyclic terpenes which comprises lecular weight dienes and mother chemical reheating vapors consisting of vaporized pinanecontaining material ata temperature above about 400 C. until isomerizationv is at least' partially complete.

. 2. A method of isomerizingpinane to a mixture of dihydroacyclic terpenes which comprises heating vapors eonsisting of vaporized pinanecontaining material at -a temperature between about 400 C. and about 700 C. uritilisomerization is at least partially complete.

3. A method of isomerizing pinane to a mixture of dihydroacyclic terpenes which comprises heating vapors consisting of vaporized pinanecontaining material at a temperature between about 450 C. and about 550 C. until isomerization is at least partially complete.

4. A method of isomerizing pinane to a mixture of dihydroacyclic terpenes which comprises heating vapors consisting of vaporized pinanecontaining "material at a temperature between about 430 C. and about 480 C. until isomerization is at least partially complete.

ture of dihydroacyclic terpenes which comprises carrying vapors consisting of vaporized pinane- Y containing material by means ,0! an inert gas through a reaction zone heated at a temperature 7 between about 400 C. and about 700 6., until pyrolysis of the pinane at a somewhat lower teml5 cdntaining material at a temp r e ween 5. A method of isomerizing pinane to a mix'- 7 asaaoec about 450' c. and about 550' c. in the presence tion is at least partially complete.

7. A method of isomerizing pinane to am:- ture of diliydroacyclic terpenes which comprises heating vapors consisting of vaporized plume-- containing material at a. temperature between about 450 C. and about 550 0.,in the presence of a mildly acidic catalytic agent, until isomer-lav oi sodium dihydro-orthophosphat'e, until isomerization is at least partially complete.

8. A method of isomerizing pinane to a mixture of dihydroacyclic terpenes which comprises heating vapors consisting of vaporized pinaneboric acid, until isomerization is at least partially complete.

ALFRED L. RBURG. 

